KR20020008054A - Process for producing a powder coating material, a powder coating material, and the use of effect pigments - Google Patents

Abstract

PURPOSE: Provided are a process for preparing a powder coating material which can be used to give powder coating materials in which the effect pigment particles are part of the powder coating particles, a powder coating material, and a use of effect pigments. CONSTITUTION: The process for preparing a powder coating material, comprises the steps of (i) processing as a melt in an extruder, at least one binder and at least one pigment and optionally, also at least one filler, additive and/or cross linker, optionally following premixing, to give a homogeneous mixture; and (ii) grinding the extrudate, after cooling, to a finished powder coating material. At least part of the pigment comprises a platelet-shaped, surface-modified effect pigment that has been coated with a low molecular mass polyethylene or polypropylene.

Description

Process for producing powder coating materials, powder coating materials, and the use of effect pigments {PROCESS FOR PRODUCING A POWDER COATING MATERIAL, A POWDER COATING MATERIAL, AND THE USE OF EFFECT PIGMENTS}

The present invention provides a homogeneous mixture by premixing the binder and pigment and, if necessary, the filler, the additive and the crosslinking agent, if necessary, into an melt in an extruder and grinding the extrudate after cooling to cool the final powder coating material. To obtain a powder coating material.

As solvent-free and environmentally-friendly coating systems, powder coating materials are of considerable importance and are preferred as solvent coating materials in various fields of use. Typically they consist of binders, pigments, fillers and, if desired, additives and crosslinkers. They exist in finely divided form and are generally applied electrostatically to many different substrates, which are cured by roasting or radiation energy on the substrates.

In the fluidized bed sintering method, the powder is kept suspended by air in the fluidization tank. When the heated substrate is immersed in the suspended powder, the polymer powder dissolves on the product. When the flow-sintered powders known to date are used to produce effect coatings, the problem of separation of effect pigments and polymers during the fluidization process can arise.

In principle, the powder coating material can be colored using all known pigments, including known effect pigments, that is to say mica-based pearl luster pigments.

Pearlescent pigments are mica plates coated with metal oxides and are used in a variety of technical fields. These are commercially available from Merck under the trade name Iriodin (registered trademark). These pigments are described, for example, in German patents and patent applications 14 67 468, 19 59 998, 20 09 566, 22 14 545, 22 15 191, 22 44 298, 23 13 331 , 25 22 572, 31 37 808, 31 37 809, 31 51 343, 31 51 356, 31 51 355, 32 11 602, 32 35 017, 33 34 598 and 35 28 256.

Powder coating materials are generally prepared by mixing the above-mentioned components in an extruder with a melt and homogenizing the mixture. A solid mass of extruded powder coating material is passed through a mill. There, the powder coating material is ground to the particle size required for the application.

However, special problems arise when platelet-shaped effect pigments are used as the pigment powder coating material. Due to the grinding process used during the preparation of the powdered pigment material, a significant portion of the pigment plate is destroyed, reducing the gloss effect. Thus far, as in the case of other pigments, it has not been possible to mix the effect pigments into the starting material for producing the powder coating material and then to extrud the mixture after extrusion.

In order to prevent destruction of the effect pigment plate, these may be ground and mixed with the powder coating material (dry blending). In this case, a disadvantage is observed in which pigment accumulates or is deleted on the surface of the object to be coated. This observation is due to the different charge patterns of the powder coated particles and the effect pigment particles. The separation problem can only be solved at least in part by an extremely expensive method, for example by a bonding method in which the mixed pigment is uniformly adhered to the surface of the powder coated particles by electrostatic forces.

German Patent No. 24 34 855 describes a method for producing metallic colored powder coating materials wherein the brushing method is used to fix the pigment plate on the surface of the pigment coated particles. The combination of the powder coating material and the effect pigment is achieved by introducing mechanical energy and possibly thermal energy.

The apparatus required to do this is very complex and reflects the high manufacturing costs for the gloss-pigment powder coating material. In addition, the gloss of the powder coating material thus obtained is often insufficient.

It is an object of the present invention to specify a method of making a powder coating material which avoids the disadvantages of the prior art described above and which can be used to obtain a powder coating material in which the effect pigment particles are part of the powder coating particles. The intention of the present invention is to obtain a coating having excellent gloss while preventing pigments from accumulating or deleting on the surface of the object to be coated as described above.

It has been surprisingly found that when surface-modifying effect pigments coated with low molecular weight polyethylene or polypropylene are used, breakage of the effect pigment plate during the grinding process as described above does not occur.

Surface-modified pearlescent pigments coated with polymeric compounds are known in particular in DE-A 43 17 019. Pigments described in this patent application include pearlescent pigments coated with polyethylene wax. Although the cited patent application claims at the outset that surface-coating and surface-modifying pigments are used in coloring varnishes, powder coating materials, paints, transfer inks, plastics, and cosmetics, it is claimed that a process for grinding coating pigments is possible. It is not. Rather, one of ordinary skill in the art should understand that, in light of the state of the art at the time, the pigment must be subsequently added to the powder coating material when used in the powder coating material as described above. Indeed, it was not expected that thin coating of the effect pigment plate with polyethylene wax or polypropylene wax would improve the mechanical stability of the pigment to such an extent that the gloss was not compromised despite the grinding process.

Accordingly, the present invention provides a homogeneous mixture by premixing the binder and the pigment and, if necessary, the filler, the additive and the crosslinking agent, if necessary, into a melt in an extruder, and after cooling the extrudate to a final powder coating material To provide a process for preparing the powder coating material described above, wherein at least a portion of the pigment fraction comprises a surface-modifying effect pigment coated with low molecular weight polyethylene or polypropylene.

The process for producing the powder coating material of the present invention is simple to implement and easy to operate. This corresponds to the conventional method of making powder coating materials. The coated effect pigments and other standard pigments and, if necessary, the binder component and the pigment component, which may include fillers, additives and crosslinkers, are thoroughly mixed using a blade mixer or a tumble mixer, for example. . During this process, the individual components can be mixed with the binder component simultaneously or sequentially. The mixture is homogenized with melt in the extruder, cooled immediately after exiting the extruder and fractionated. In the mill, the powder coating material is ground to final fines.

The powder coating material obtained by the process of the invention provides significant advantages over the prior art. That is, no separation occurs, so that the application reliability is increased. The manufacturing cost is low because no bonding process or similar complex process is required. It is also possible to produce tribologically applicable powder coating materials which have not been possible until now. It is also possible to produce powder coating concentrates containing effect pigments according to the process of the invention.

Additionally, the present invention provides a powder coating material comprising a binder and a pigment and, if desired, a filler, an additive, and a crosslinking agent, wherein at least a portion of the pigment fraction is coated with low molecular weight polyethylene or polypropylene. It contains a modifying effect pigment.

The effect pigment is advantageously a mica pigment coated one or more times with a metal oxide (pearl polished pigment). By using this pigment, optimal results are achieved in terms of gloss and effectiveness. However, other effect pigments that can be used are coated Al ₂ O ₃ plates, bismuth oxychloride (BiOCl), aluminum flakes, Variocrom® or Paloocrom® pigments from BASF. , LCP pigments (liquid crystal polymer pigments), coated glass flakes or multilayer pigments of 3 to 9 layers, preferably 3, 5 or 7 layers.

In addition, effect gloss pigments which are preferably used are prepared by chemical or physical deposition (CVD; chemical vapor deposition or PVD; physical vapor deposition) in the gas phase or by deposition in aqueous solution.

The effect pigment content is from 0.1 to 50% by weight, based on the sum of the components. Smaller amounts do not show enough effect, and similarly larger amounts lose the effect. The effect pigment content is preferably from 0.5 to 30% by weight, in particular from 0.5 to 10% by weight, very particularly from 1 to 7% by weight, based on the total weight of the powder coating material.

With regard to the powder coating materials of the present invention it is possible, in general, to use all commercially available powder coating materials based on reactive epoxides, polyesters, polyacrylates or polyurethanes or other polymers which may be reactive and thermoplastic. Particular preference is given to polyester powder coating materials, polyacrylate powder coating materials, polyurethane powder coating materials, epoxy powder coating materials or polyester-epoxy powder coating materials.

The effect pigments are covered with 15 to 50% by weight, more preferably 15 to 40% by weight, particularly preferably 15 to 35% by weight of polyethylene or polypropylene, based on the total weight of the effect pigment and the respective polyethylene or polypropylene Is advantageous.

Low molecular weight polyethylene or polypropylene used is advantageously polyethylene or polypropylene having a molecular weight of 1,000 to 20,000 daltons.

It is advantageous that the effect pigments have a particle size of 5 to 200 μm. When the effect pigment is a pearlescent pigment, it has a particle size of 5 to 100 mu m, preferably 10 to 60 mu m.

The powder coating materials of the present invention may be formed of any desired substrate materials, such as iron and steel, aluminum, copper, bronze, brass, metal and metal foils, and conductive modified surfaces such as glass, ceramics and concrete for decorative and / or protective purposes. And non-conductive surfaces such as, for example, wood, glass, ceramics, plastics, inorganic building materials or other materials such as furniture.

In order to improve the surface quality, it is also possible to apply one or more transparent coatings applied to the powder coating to the powder coating, which generally results in an overall improvement in the fastness of the coating in addition to the appearance. However, a transparent final coat is not necessary.

The present invention also provides a surface-modifying effect coated with low molecular weight polyethylene or polypropylene for producing powder coating materials comprising binders and pigments and mixtures obtained by extruding and pulverizing fillers, additives and curing agents as needed. It provides a use of the pigment.

Hereinafter, an Example and a comparative example are given and this invention is illustrated.

Example

In the preparation of the premixed, extruded and ground powder coating materials, 5% of Iriodine 163 and all other necessary raw materials coated with low molecular weight polyethylene were introduced. This was then conventionally applied by electrostatic means.

Comparative example

In the preparation of the premixed, extruded and ground powder coating materials, 5% of Iriodine 163 and all other necessary raw materials were introduced. This was then conventionally applied by electrostatic means.

As a result of visual comparison of the coated metal specimen panel in the above example with the specimen in the comparative example, the comparative example shows virtually no pearl gloss or brilliance effect, whereas in the examples the gloss and brilliance effect is good to very high. Showed good.

Powder coating materials comprising surface-modifying effect pigments coated at least in part with low molecular weight polyethylene or polypropylene according to the invention provide excellent gloss effects.

Claims (9)

After pre-mixing the binder and the pigment and, if necessary, the filler, the additive and the crosslinking agent, if necessary, it is processed into a melt in an extruder to obtain a homogeneous mixture, and after cooling, the extrudate is pulverized into a final powder coating material to coat the powder. A method of making a material, wherein at least a portion of the pigment fraction comprises a platelet-shaped surface-modifying effect pigment coated with low molecular weight polyethylene or polypropylene. The method of claim 1, Mica pigments coated with iron oxide and / or titanium dioxide, coated SiO ₂ plates, metal oxide plates coated one or more times, bismuth oxychloride plates, aluminum flakes, LCP pigment plates, coated glass flakes and / or multilayer pigments Use as an effect pigment. The method according to claim 1 or 2, Wherein the content of the effect pigment is from 0.1 to 50% by weight, based on the sum of the components. The method according to any one of claims 1 to 3, The binder is polyester, polyacrylate, polyurethane, epoxide or polyester-epoxide. The method according to any one of claims 1 to 4, The effect pigment is coated with 15 to 50% by weight polyethylene or polypropylene, based on the weight of the effect pigment. The method according to any one of claims 1 to 5, Characterized in that the molecular weight of polyethylene or polypropylene is from 1,000 to 20,000 daltons. The method according to any one of claims 1 to 6, And wherein the effect pigment has a particle size of 5 to 200 μm. A powder coating material comprising an extrusion mixture, obtained by extruding a binder and a pigment and, if desired, a filler, an additive, and a crosslinking agent, wherein at least a portion of the pigment fraction is coated with a low molecular weight polyethylene or polypropylene- A substance characterized by comprising a modifying effect pigment. The use of surface-modifying effect pigments coated with low molecular weight polyethylene or polypropylene for producing powder coating materials comprising binders and pigments and, optionally, mixtures obtained by extruding and grinding the fillers, additives and curing agents.